Accompanying the advance of an aging society, osteoporosis, which reduces bone density and contributes to easy bone fracture with the advance of age, is becoming a serious problem. It has been revealed that osteoporosis causes a fracture of lumber vertebra or thighbone due to reduction of the bone mineral content and thereby becomes a cause for bedridden state. Particularly, females are apt to get osteoporosis due to rapid reduction of the bone mineral content caused by the estrogen secretion reduction with menopause. Regarding the treatment of osteoporosis, since it is not easy to restore the once reduced bone mineral content, it is considered to be very important to prevent osteoporosis from a younger age or to prevent the rapid reduction of the bone mineral content after menopause.
In order to prevent osteoporosis, it is important to increase bone mass from a younger stage, and for this purpose, it is necessary to take care of appropriate physical exercise and daily ingesting foods. In having meals, it is important to ingest much dairy products and fishes which are rich in calcium. In addition, use of vitamin K (e.g., see Patent Reference 1), oligosaccharides and minerals (e.g., see Patent Reference 2), casein phosphopeptide (e.g., see Patent Reference 3), soybean isoflavone (e.g., see Non-patent Reference 1) or vitamin D and the like as so-called healthy food, has been recommended recently as they are effective.
Particularly, equol, which is a metabolite of a kind of soybean isoflavone, daidzein, is isoflavones having various characteristics such as a high antioxidant activity and a high estrogen activity, and has already been disclosed as an agent for treating osteoporosis (Patent Reference 4). In addition, as the functions of equol, a plasma cholesterol lowering function, suppression of breast cancer or prostatic cancer and the like have been reported (Non-patent Reference 2).
However, since the metabolism from daidzein to equol is mainly carried out by intestinal bacteria, it is known that the metabolism is largely influenced by individual intestinal bacterial flora and the production quantity varies with the difference in sex and the difference in the human race. Actually, it has been reported that approximately from 60 to 70% of Europeans and Americans have a low ability to produce equol. Accordingly, DFA III (difructose-dianhydride III) (Non-patent Reference 3) and a fructo-oligosaccharide (Non-patent Reference 4) have so far been known as the substances which accelerate production of equol.
Patent Reference 1: JP-A-10-056959
Patent Reference 2: JP-A-7-252156
Patent Reference 3: JP-A-5-284939
Non-patent Reference 1: “Daizu Tanpakushitsu Kenkyu (Soybean Protein Studies)”, written by Kazuhiko Kato and Hiromi Suemitsu, published by Fuji Foundation for Protein Research, Vol. 5, p. 134-137 (2002)
Patent Reference 4: JP-A-2005-232074
Non-patent Reference 2: “Kagaku To Seibutsu (Chemistry and Biology)”, published by Japan Society for Bioscience, Biotechnology and Agrochemistry, Vol. 44, No. 3, p. 151-153 (2006)
Non-patent Reference 3: Abstract of the 49th Annual Meeting of Japan Society for Bioscience, Biotechnology and Agrochemistry, published by Japan Society for Bioscience, Biotechnology and Agrochemistry, p. 97 (2005)
Non-patent Reference 4: Abstract of the 56th Annual Meeting of Japanese Society of Nutrition and Food Science, published by Japanese Society of Nutrition and Food Science, p. 138 (2002)